Dominic Stone
The human face has about 20 main facial muscles that are essential for chewing and making facial expressions. The muscles of mastication, or the act of chewing, involve adduction and lateral motion of the jaw bone. The four main muscles of mastication are the masseter, temporalis, and pterygoid muscles. The masseter muscle, the most powerful muscle of mastication, elevates the jaw and assists in closing the mouth. The temporalis muscle assists in side-to-side movement during chewing, closing the mouth, and grinding movements. The pterygoid muscles assist in opening the jaw, clenching, moving side-to-side, and rotating and projecting the lower jaw.
| Characteristics | Values |
|---|---|
| Number of muscles involved in chewing | 20 |
| Muscle that assists in opening the jaw | Lateral pterygoid |
| Muscle that assists in closing the jaw | Masseter |
| Muscle that assists in side-to-side movement | Temporalis |
| Muscle that assists in grinding movements | Temporalis |
| Muscle that assists in clenching | Pterygoid |
| Muscle that assists in moving food to the back of the mouth | Tongue |
| Muscle that assists in swallowing | Tongue |
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What You'll Learn
The masseter muscle
The masseter is primarily responsible for the elevation of the mandible, causing a powerful jaw closure. This elevation occurs during the closing of the jaws. The masseter also assists in some protraction of the mandible, which is the forward movement of the jaw. The deep fibres of the masseter function to retract the mandible, while the superficial fibres function to protrude the mandible. The deep fibres also help to stabilise the temporomandibular joint.
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The temporalis muscle
Tension in the temporalis muscle can cause pain in the temporal area and is associated with jaw pain and headaches.
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The lateral pterygoid muscle
The two bellies of the lateral pterygoid muscle were traditionally believed to have opposing functions due to their different anterior insertions. The inferior belly, which is much wider than the superior belly, was thought to depress, protrude, and deviate the mandible to the contralateral side. Meanwhile, the superior belly was believed to elevate the mandible to close the mouth. However, recent studies suggest that the two bellies may function similarly, with the superior belly also becoming active during mouth opening, protrusion, and contralateral deviation.
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The medial pterygoid muscle
The unilateral contraction of the medial pterygoid muscle causes a slight medial rotation of the mandible. When this occurs simultaneously with the contraction of the ipsilateral lateral pterygoid, it results in a noticeable movement where the same-sided part of the mandible swings anteriorly and medially. The bilateral contraction of the medial pterygoid muscle, on the other hand, elevates and protrudes the mandible. These movements are crucial for the act of chewing, especially when the maxillary and mandibular teeth are close together.
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The tongue
The eight muscles of the tongue are classified as either intrinsic or extrinsic. The four intrinsic muscles change the shape of the tongue and are not attached to any bone. The four extrinsic muscles change the tongue's position and are anchored to bone. Their main functions include allowing the tongue to protrude, retract, and move side to side.
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Frequently asked questions
The muscles involved in chewing are the masseter, temporalis, lateral pterygoid, and medial pterygoid.
The masseter muscle is the most powerful muscle involved in chewing. It elevates the jaw, closing the mouth.
The temporalis muscle assists in side-to-side movement during chewing, closing the mouth, and grinding movements.
